Gear crowning machine



June 6, 1944. R, s, DRUMMND 2,350,882

GEAR CROWNING MACHINE Filed Dec. 12, 1938 3 Sheets-Sheet 5 S2 LI- 2 L.

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(9 INVENTOR LL.

ROBERT $.DRUMMOND A TTORNEYS Patented June 6 1944 UNITED STATES PATENT OFFICE Gm cnowNING mcnmn Robert s. Drummond, Detroit, ma. Application December 12, 1938, Serial No. 245,324

19 Claims.

machine provides a work arbor and a tool arbor which are relatively adjustable so that they may be set with their axes crossed, preferably at an angle of less than A tool in the form of a gear having cutting edges provided on the work-- ing faces of its teeth is supported on the tool arbor. The helix angle of the teeth of the tool are selected such that the gear to be finished and the tool mesh with their axes crossed as indicated.

Means are provided for positively rotating one of the aforementioned arbors, the other of said arbors being mounted for free rotation. Due to the crossed axes relationship a cross sliding action between the tool and the work piece is developed which removes metal from the working faces of the teeth of the work piece. Due also to the crossed axial relationship the instantaneous contact between the teeth of the tool and the teeth of the work piece is limited theoretically to the point; and practically, due to deformation of the metal and provision of the cutting edges, to a limited area. During rotation of the tool and work piece the point of instantaneous contact moves from top to bottom of the gear teeth. 1

both of said axes.

In the present embodiment I have illustrated this translation as resulting from an axial reciprocation of the work arbor, although if desired the work arbor may be translated in a direction transverse to its-axis, or the gear arbor may be translated to cause a corresponding relative translation.

The axes of the work piece and tool are retained in rigidly spaced relation during such translation with the result that a predetermined amount of metal is shaved from the working faces of the gear teeth. In order that the machine may be fully automatically operated, I provide means which causes the axes of work piece to be relatively fed towards each other at the end of each translation. The mechanism for obtaining this result will be described subsequently in detail, and is further clearly set forth in my copending application referred to above.

It will be understood that the operation of the machine as thus far described would result in accurately finishing the teeth of the work gear uniformly from end to end. In many cases it is desirable to provide a slight crowning effect to the teeth of the .work gear. As is well understood, crown teeth have their bearing with teeth of a meshing gear shifted \centrally thereof whichpermits silent gear action, even though slight misalignment of the gear supporting shafts is present. In addition crowned gear teeth operate more silently even though they have properly aligned axes since engaging teeth come into contact more gradually. In some cases, also, crowned teeth are desirable to allow angular setting of mating parts.

In order to provide the finished gear teeth with a predetermined crown effect, I provide additional means for gradually varying the normal spacing of the work arbor and the tool arbor in accordance with the translation.

The parent case which is mentioned relates to a gear tooth which is finished so that it is crowned at its mid-portion and has both ends gradually relieved. This effect as will be evident may. be obtained in the present machine by causing the work arbor to be raised and lowered relative to the tool arbor in timed relation to the translation, the timed relation being such that the work arbor is elevated at both ends of a translation stroke and is at its lowermost position in mid stroke of each translation.

With the foregoing general description in mind it is an object of the present invention to provide a machine for crowning gear teeth by gradually varying the distance between the work arbor and the tool arbor in accordance with relative translation.

It is a further object of the present invention to provide a machine for crowning gear teeth in which the work arbor and tool arbor are caused gradually to approach and separate in accordance with relative translation and without disturbing the orientation of said axes.

It is a further object of the present invention to provide a machine for relatively moving a work arbor and a tool arbor to provide crowned teeth in combination with means for providing feeding adjustments between the arbors at the end of a translation.

It is a further object of the present invention to provide a machine for crowning gears by the gear and gradually varying the spacing between tool and which adjustable means are provided for limiting the crowningeifect to a predetermined portion of the endsof the gear teeth.

Other objects of the invention will be apparent as the description proceeds and when taken in conjunction. with the accompanying drawings, and wherein Fig. 1 is a side elevation with parts broken away showing a gear finishing machine;

Fig. 2 is an enlarged rear elevation of the table "61 my gear finishing machine with parts broken away;

Fig.3 is a section on the line 3-3, Fig. 2;

Fig. 4 is a view similar to Fig. 3 in which a V crowning attachment has been added to the actuating mechanism;

Fig. 5 is a section on the line 5-5, Fig. 4;

Fig. 6 is a section on the line 6-6, Fig. 4;

Fig. 7 is a vertical section of a modified crowning control mechanism;

Fig. 8 is a section on the line 8-8, Fig. 7; and

Figs. 9, 10 and 11 are front elevations of the parts in section showing modified forms of crowning mechanism.

In Figs. 1, 2 and 3 I have illustrated a gear finishing machine having a frame In which supports a tool head The tool head is mounted for adjustment about a vereical axis relative to an overhanging portion I! of the frame. Motor i3 is carried by the portion l2 of the frame and is adapted to drive a tool which is rotatably supported in the tool head through suitable driving mechanism I4. Details of this driving mechanism form no part of the present invention and are fully described in my copending application referred to above.

The frame l3 has a forwardly projecting knee I5 above which is supported for vertical adjustment a table |6. The table 6 is accurately guided for vertical adjustment relative to the frame H1 in suitable cooperating ways indicatedin part in Fig. 1 at H.

Carried by the table l6 and horizontally adjustable thereon in ways I3 is a carriage l9 having a support thereon for a gear arbor indicated generally at 2 I A motor 22 is secured to the table It by a I bracket II, the motor being received within the hollow frame l9 and connected to suitable driving mechanism carried by the table l6 through a slot 23 formed in the forward face of a frame It. As will now be described in detail the motor 22 is adapted to reciprocate the carriage 9 horizontally and to elevate the table I6 periodically, and also as will subsequently be described to control vertical motion of the table 16 in order to crown the teeth of the work piece.

Motor 22, as seen in Fig. 1, is connected through suitable speed control mechanism 24 and flexible coupling 25 to a gear 26. Gear 26 as indicated in Fig. 2 is adapted to mesh with and drive a gear 21, which in turn drives a coaxial bevel gear 23. The bevel gear 28 in turn meshes with and drives a second bevel gear 29 secured to a vertically extending shaft 30. Shaft 30 has keyed or otherwise secured thereto a bevel gear 3| and a worm 32.

The horizontally movable carriage l9 has a depending lug 33 which is internally threaded to cooperate with a threaded horizontal feed screw 34 joumalled for rotation in the vertically adjustable table. As will be apparent from Fig. 2, rotation of the feed screw 34 will cause the slow translation of the carriage l9. Feed screw 34 has keyed or otherwise secured thereto a bevel gear 35 meshing with bevel gear 3|. From the foregoing, it will be apparent that operation of the motor 22 through the medium of gears 26. 21, 26, 29, 3| and 35 causes a slow translation of the carriage l9 relative to the table IS.

The worm 32, previously referred to, is adapted to mesh with and drive a worm gear 36 which is connected to a shaft 31. The shaft 31, as best seen in Fig. 3, has connected thereto a gear 38 adapted to mesh with a gear 39 carried by a shaft 40, the shaft 40 also carrying a feed actuating device 4|. Feed actuating device 4| comprises a pair of radially extending arms 42 which are adapted to engage a lever 43 pivoted at 44. Lever 43 has connected to its free end a link 45 which in turn is connected to a feeding device indlcated generally at 46.

The feeding device 46 includes a spring pressed dog 41 which is adapted to cooperate unidirectionally with a ratchet wheel 46 carried by a shaft 49. An adjustable sheet metal mask 50 is movable with the ratchet wheel 43 and, as will be evident, when the mask reaches the spring pressed dog '41 the dog 41 will be ineffective to further actuate the ratchet wheel. The mask 53 has a portion (not shown in Fig. 3) which is adapted to overlie the teeth of the ratchet wheel.

The shaft 49 referred to above is shown in Fig.

3 and its driving connection to the work table It is best seen in Fig. 2. The shaft 49 carries at its free end a bevel pinion 5| which in turn meshes with a bevel gear 52 keyed or otherwise secured to a vertical shaft 53. The shaft 53 has a table feed screw portion 54 formed thereon or attached thereto. In addition the shaft 53 is adapted to support the table l6 through the medium of a flange 55 upon which is engaged a transverse partition 56 of the table, suitable bearings 51 being provided.

As will be apparent from the foregoing, rotation of the motor in addition to causing a translation of the carriage l9 rotates feed actuating device 4| through the medium of worm 32 and worm gear 36. Rotation of the table feed actuating device 4| causes periodical shifting of the spring pressed dog 41 and a corresponding slight rotation of the ratchet wheel 43 and shaft 49 and hence of table feed screw 54. Table feed actuating mechanism 4| is adjustable as a unit and actuating arms 42 are separately. adjustable to time the table feed actuation so as to occur substantially at the end of horizontal translation of the carriage l9.

In addition to the automatic feeding mechanism previously described, manual means are pro- .vided for raising and lowering the work table l6.

These means take the form of a hand wheel 53 adapted to rotate the shaft 53 through the medium of inter-meshing bevel gears 59 and60.

Referring again to Fig. 1, the knee l5 of the frame is provided with a table feed nut 6| in which the threaded portion of the table feed screw 54 is threadedly engaged. As will be evident, rotation of the shaft 53 and hence the feed screw 54 results in vertical adjustment of the table I.

In Figs. 4, 5 and 6 I have illustrated an attachment to the machine illustrated in Figs. 1, 2 and 3 for imparting a crowning motion to the work spindle. As best seen in Fig. 4, a plate 62 having an arcuate slot 63 of predetermined contour is attached to the disk 4| carried by the shaft 40.

The link 48 pivoted as before at 44 is provided with an eccentrically adjustable roller 84 which is received within slot". Rotation of the shaft 48 which is occasioned through worm 82 and worm gear 88 as previously described results in a controlled oscillation of the lever 48 about its pivot Point 44.

It will be understood that in order to bring about reversal of translation of the carriage I! the motor 22 is reversed by suitable switching mechanism, which forms no part of the present invention.

A crowning plate '85 is attached to the ratchet wheel 48 and is secured thereto in adjustable position as by bolts 88. A mask element 81 having a portion 88 adapted to cover the ratchet teeth adjacent the spring pressed dog 41 is provided. Link 45 is pivotally secured to an actuator 89 which carries the spring pressed dog 41, and in addition a plunger 19 adapted to be received within the recess 1| in plate 85. Actuator 89 is freely supported for movement about the shaft 49 as indicated in Fig. 6.

The spring pressed plunger 18 is connected to a control member 12 which may be shifted to cause plunger 19 to engage recess 1| or to be withdrawn therefrom as desired.

The mask 61 may be adjusted to render completely inactive the dog 41, or may be otherwise adjusted as will now be explained.

iAssume first that the portion 88 is set to expose only one ratchet tooth on disk 48. Plunger 18 will be withdrawn from recess 1|, and is adapted to ride over the smooth periphery of disk 85. Movement of the link 45 will be ineffective to cause elevation of the table until the carriage approaches the end of a stroke. At this time, the dog 41 will engage the ratchet wheel 48 and elevate the table, for example a thousandth of an inch. The table will remain stationary until the carriage approaches the opposite end of stroke, whereupon a further small up feed occurs. Ultimately the plunger 19 reaches recess 1| and drops therein as the table is again elevated. Further reciprocation of the table causes a gradual controlled up and down table feed. This results in crowning the ends only of the gear teeth, the gear and tool moving into a slight clearance relation in mid stroke of the carriage.

By adjusting the mask 81, the extent of the crowning action, measured centrally from each end of the gear teeth, may be controlled. If the mask 81 is adjusted so as to be entirely ineffective, crowning takes place, after engagement between the plunger and recess 1|, over the entire width (from end to end) of the gear teeth. The function of the plunger 10 and recess 1|, when engaged, is to provide a down feed of table IS on downward motion of link 45. When plunger 10 and recess 1| are engaged, solely upward feeding motion as opposed to alternately up and down crowning motion, is terminated.

With the mask 81 adjusted to render completely inoperative the spring pressed dog 41 and with the spring pressed plunger 18 shifted to engage the recess 1| of plate 85, the operation of the crowning attachment is as follows: The motor 22 rotates worm 32 and bevel gear 8|. Rotation of the bevel gear 3| results eventually in rotation of carriage feed screw 34 and a corresponding horizontal translation of the carriage l9. Rotation of the worm 32 results in a timed slow rotation of the disk 4| and hence of the slotted cam plate 82. The follower 84 causes the lever 48 to be slowly oscillated about its axis 44 which results in a back and forward oscillation of the disk 55. Since the upon reversal of the'motor 22, and in addition reverses as the follower 84 passes the mid-point of the slot 88. It will be understood of course that the cam plate 82 is adjusted so that the follower 54 is in mid-position between the ends of the slot 88 when the tool is engaged with the mid-portion of the teeth of the work gear. It will also be evident that by substituting cam plates for slots in various formations a crowning action predetermined as to amount of stock removal and extent from end to end of the work gear teeth may be obtained. When it is desired to omit the crowning motion and to return to automatic feed, cam plate 82 is removed and arms 42 are substituted therefor. At the same time mask 81 is adjusted so as to render operative the spring pressed dog 41 and in addition actuatingmember 12 is shifted so as to disengage plunger 18 from recess 1|,

In Figs. 7 and 8 I have illustrated a modification of the crowning attachment. In place of providing a table feed nut 8| bolted to the knee l5 of the frame, I provide a movable feed screw nut 15 which is provided with flanges 18 and 11. The nut 15 is positioned in an aperture 18 formed in the top of the knee l5 and flange 18 is adapted to support the nut as shown in Fig. '7. Pins 19 are provided on the knee l5 and engage in opposed-recesses 88 formed in the flange 18. Pins 19 and recesses prevent rotation of the nut 15 but permit vertical movement thereof. Received within the knee I5 is the actuating mechanism for shifting the nut 15. I have indicated this actuating mechanism as originating in a cam 8| which is driven in timed relation to translation. Cam 8|, for example, may be rotated by appropriate mechanism including a flexible driving shaft, such as that indicated in Fig. 10, later to be described.

As an alternative, if desired, link 45, previously referred to, may be extended downwardly and be appropriately connected to the shaft supporting the cam 8|. Secured for vertical adjustment as by clamping means 82 and slot 83 I provide a bracket 84 on which is mounted for horizontal adjustment a pivot member 85. In Fig. 7 I have indicated member 85 as slidable in suit able ways formed on a horizontal portion 88 of the bracket 84 and adjustable thereon by means of set screws 81. Pivot member 85 is provided with a pin 88. A lever 89 is provided at its midportion with an elongated slot 99 for the adjustable reception of the pivot pin 88. Lever 89 has a portion 9| adapted to engage cam 8|. The opposite end of the lever 89 is bifurcated as indicated at 92, the two arms thus provided being adapted to engage the under surface of the flange 11.

As will be apparent upon rotation of cam 8| in timed relation to the horizontal translation of the carriage IS the lever 89 will be oscillated about its pivot point 88. By adjusting the bracket 84 vertically the bifurcated arms 92 of the lever 89 may be in continuous engagement with the flange 11 which will result as is obvious in a continuous vertical movement of the nut 15 during translation. If desired the bracket 84 may be lowered so that the arms 92 engage the under surface of the flange 11 only adjacent the ends of the translation of the carriage. This will-result in finishing a gear tooth which is crowned only for a predetermined amount adfacent the ends of its teeth.

By adjusting thepivot member 96 horizontally theamplitude of crowning motion may be adjusted. It will be understood that normally the crowning motion to be imparted is extremely slight, on the order of a few ten-thousandths of an inch.

It will be noted that the crowning adjustment imparted to the nut 16 results in a vertical adjustment of the table It and is entirely independ-* the carriage feed screw 34. At this time the table 7 I6 is moved vertically by movement of feed nut I5. At the end of each translation of the carriage I9 a feeding motion is superimposed on the table I6 by a slight abrupt rotation of the shaft 53 and table feed screw 54. As previously stated,

automatic mechanism is provided to reverse the;

motor 22 at the end of each translation. .Reversal of the motor initiates a reverse translation of the table which in turn results in a horizontal translation of the gear upon which is super imposed the crowning motion due to the vertical movement of the nut I5. Means are provided to continue translations a predetermined number of times and then to bring the entire mechanismto rest.

In Fig. 9 I have illustrated a somewhat different embodiment of my invention in which the table feed nut 95 is supported for rotation on the knee I5. A lever 96 is pivoted as indicated at 91 to a vertically adjustable bracket 98.

Springs 99 are provided to retain lever 96 in midposition unless otherwise actuated. Attached to 'the lower end of the lever 96 is a pivoted link I which engages arm IOI operatively connected to adjusting worm I02. ,Nut 95 is provided at its periphery with a toothed portion adapted to mesh with worm I02. Adjustably carried by the horizontally movable carriage I9 are a pair of abutments I03 which are adjustable as indicated to control the extent of crowning action. The rate of crowning may be varied by vertically adjustingthe bracket 98 to move the pivot point 91 relative to the ends of lever 96. Conventional means, such as an elongated slot in the lever 96 or a plurality of closely spaced apertures for receiving pivot pins may be provided to permit this adjustment.

It will be evident that upon horizontal translation of carriage I9 the lever '96 will be pivoted about the point 91. Through the medium of the link I00 the arm III will thus be rotated and cause a corresponding rotation of the worm I02. It will be noted that movement of the lever 96 in either direction from its mid-position results in the same movement of the worm I 02.

In Fig. I have illustrated a somewhat different embodiment of my invention in which table feed nut I I4 engages feed screw 54, and has a pair of diametrically projecting pins I05 supported within elongated slots in a bifurcated or split portion of a lever I09. The lever is pivoted rotation the lever I06 is effective to move the table feed nut vertically, thus imparting a corresponding motion to the feed screw it and thus.

imposing upon the horizontal translation of the carriage I9 the crowning movement. It will be understood that this crowning motion is superimposed'without eflecting the periodical feeding motion which results from intermittent slight rotation of the table feed screw 64 through the mechanism illustrated in Figs. 2 and 3.

In Fig. 11 I have shown a somewhat diflerent mechanism for imparting a crowning motion to the table I6. A motor I20 is connected to a worm I2I adapted to mesh with worm gear teeth formed on the table feed nut I22. A switch I23 is carried by the table and is adapted to be engaged by adjustable abutments I24 carried by the carriage. Springs I25 normally retain switch arm I22 in intermediate position. Suitable means (not iilustrated) is adapted to reverse rotation of the motor I20 upon reversal of translation of the carriage I 9. If desired, the means for reversing motor 22 may be employed for this purpose. The switch actuated by the switch arm I 23 is constructed and arranged so that movement ofthe switch arm I23 to intermediate position sets up a reversing circuit to the motor I20 such that upon actuation of the switch arm I22 in the opposite direction the motor will be operated in a proper direction. This results in operation of the motor in a direction to elevate feed screw 54 during translation of the table I 9 away from midposition and an opposite rotation of the motor I20 adapted to result in a lowering of the feed screw 54 after the carriage I9 returns from limiting to mid-position.

I have found that the crowned eilect imparted to gears by this type of machine, namely one in which the axes of the work piece and tool are caused to proceed and recede in accordance with translation and without disturbing their orientation imparts a superior crowned effect to the gear teeth. The crowning appears as a uniform lowering of the profile adjacent the ends of the gear teeth. r

The foregoing detailed description has been given for clearness and understanding only, and no unnecessary limitations should be understood therefrom, but the appended claims should be construed as broadly as permissible in view of the prior art.

What I claim as my invention is:

1. A machine for finishing gears comprising a gear arbor, a tool arbor, means for supporting said arbors with their axes crossed at an angle less than 30, means for rotating one of said arbors, means for relatively translating said arbors in a plane parallel to the axes of both of said said arbors with their axes crossed at anangle less than 30, means for rotating one of said arbors, means for relatively translating said arbors in a plane parallel to the axes of both of said arbors, feed screw and nut elements for feeding one of said arbors toward the other, means automatically operable in accordance with said translation for gradually rotating one of said elements relative to the other successively in opposite directions.

3. A machine for finishing gears comprising a gear arbor, a tool arbor, means for supporting said arbors with their axes crossed at an angle less than 30, means for rotating one of said arbors, means for relatively translating said arbors in a plane parallel to the axes of both of said arbors, feed screw and nut elements for feeding one of said arbors toward the other, means auto- .matically operable in accordance with said translation for gradually rotating one of said elements relative to the other, said last means being efi'ective to reverse said rotation at the ends and substantially intermediate the ends of said translations.

4. A machine for finishing gears comprising a,

gear arbor, a tool arbor, means for supporting said arbors with their axes crossed at an angle less than 30, means for rotating one of said arbors, means for relatively translating said arbors in a plane parallel to the axes of both of said arbors, feed screw and nut elements for feeding one of said arbors toward the other, means operable in accordance with said translation for rotating one of said elements relative of the other, and other means operable in accordance with said translation for bodily moving said nut element in a direction parallel to the axis of said feed screw.

5. A machine for finishing gears comprising a gear arbor, a tool arbor, means for supporting said arbors with their axes crossed at an angle less than 30, means for rotating one of said arbors, means for relatively translating said arbors in a plane parallel to the axes of. both of said arbors, feed screw and nut elements for feeding one of said arbors toward the other, means operable in accordance with said translation for rotating one of said elements relative of the other, and other means operable in accordance with said translation for bodily moving said nut element in a direction parallel to the axis of said feed screw, said last means being adjustable to be effective during only a predetermined portion of said translation.

6. Amachine for finishing gears comprising a gear arbor, a tool arbor, means for supporting said arbors with their axes crossed at an angle less than 30, means for rotating one of said arbors, means for relatively translating said arbors in a plane parallel to the axes of .both of said arbors, means automatically operable in response to said translation for imposing two separate motions on said translation, one of said motions being an abrupt feed in a direction perpendicular to the plane of translation substantially at the end of a translation, and the other being a gradual motion in the same direction as said feed, and timed in accordance with said translation.

7. A machine for finishing gears comprising a gear arbor, a tool arbor, means for supporting said arbors with their axes crosses at an angle less than 30, means for rotating one of said arbors, means for relatively translating said arbors in a plane parallel to the axes of both of said arbors,

means automatically operable in response to said translation for imposing two separate motions on said translation. one of said motions being an abrupt feed in a direction perpendicular to the plane of translation substantially at the end of a translation, and the other being a gradual motion in the same direction as said feed, and timed in accordance with said translation, and means for separately adjusting said imposed motions.

8. A machine for finishing gears comprising a gear arbor, a tool arbor, means for supporting said arbors with their axes crossed at an angle less than 30, means for rotating one of said arbors, means for relatively translating said arbors in a plane parallel to the axes of both of said arbors, means automatically operable in response to said translation for imposing two separate motions on said translation, one of said motions being an abrupt feed in a direction perpendicular to the plane of translation substantially at the end of a translation, and the other being a gradualmotion in the same direction as said feed, and timed in accordance with said translation, and means for varying the amount, and duration relative to translati n, of said last mentioned motion. ,5; 9. A m chine for finishing gears comprising a gear arbor, a tool arbor, means for supporting said arbors with their axes crossed at an angle less than 30, means for rotating one of said arbo'rs, means for relatively translating said arbors in a plane parallel to the axes of both of said arbors to shift the bearing of said tool alternately from a mid position to opposite ends of said gear teeth, automatic means effective as said bearing shifts from mid position toward either end for causing said arbors to approach gradually, and effective only after a predetermined number of translations for causing said arbors to separate gradually as said bearing shifts from. either end centrally on said gear teeth.

10. A machine for finishing gears comprising a gear arbor, a tool arbor, means for supporting said arbors with their axes crossed at an angle less than 30, means for rotating one of said arbors, means for relatively translating said arbors in a plane parallel to the axes of both of said arbors to shift the bearing of said tool aitemately from a mid position to opposite ends of said gear teeth, automatic means effective as said bearing shifts from mid position toward either end for causing said arbors to approach gradually, and eflective only after a predetermined number of translations for causing said arbors to separate gradually as said bearing shifts from either end centrally on said gear teeth, the rate of approach and separation of said arbors being the same.

11. A machine for finishing gears comprising a gear arbor, a tool arbor, means for supporting said arbors with their axes crossed at an angle less than 30, means for rotating one of said arbors, means for relatively translating said arbors in a plane parallel to the axes of both of said arbors to shift the bearing of said tool alternately from a mid position to opposite ends of said gear teeth, automatic means effective as said bearing shifts from mid position toward either end for. causing said arbors to approach gradually, and effective only after a predetermined number of translations for causing said arbors to separate gradually as said bearing shifts from either end centrally on said gear teeth, said automatic means being adjustable to select the point in translation at which said approach is initiated.

12. A machine for finishing gears comprising a gear arbor, a tool arbor, means for supporting said arbors withtheir axes crossed at an angle less than 30, means for rotating one of said arbors, means for relatively. translating said arbors in a plane parallel to the axes of both of said arbors to shift the bearing of said tool alternately from a mid position to opposite ends of said gear teeth, automatic means effective as said bearing shifts from mid position toward either end for causing said arbors to approach gradually, and effective only after a predetermined number of translations for causing said arbors to separate gradually as said bearing shifts from either end centrally on said gear teeth, said automatic means being adjustable to select the point in translation at which said approach is initiated, said last means including means effective to cause separation of said arbors continuously as said bearing shifts from either end of said gear teeth to mid position irrespective of the point in translation at which approach of the arbors began.

13. A machine for finishing gears comprising a gear arbor, a tool arbor, means for supporting said arbors with their axes crossed at an angle less than 30, means for rotating one of said arbors, means for relatively translating said arbors in a plane parallel to the axes of both of said arbors to shift the bearing of said tool alternately from mid position toward either end of said gear teeth, means operable in accordance with said translation for causing said arbors to approach by increments, and other means for causing said arbors to approach gradually as said bearing shifts from mid position toward either end of said gear teeth and for causing said arbors to separate gradually as said bearing shifts from either end 01' said gear teeth centrally.

14. A machine for finishing gears comprising a gear. arbor, a tool arbor, means for supporting said arbors with their axes crossed at an angle less than 30, means for rotating one of said arbors, means for relatively translating said arbors in a plane parallel to the axes of both oi'said arbors to shift the bearing of said tool alternately from mid position toward either end of said gear teeth, means operable in accordance with said translation for causing said arbors to approach by increments, and other means for causing said arbors to approach gradually as said bearing shifts from mid position toward either end of saidgear teeth and for causing said arbors to separate gradually as. said bearing shifts from either end of said gear teeth centrally, the rate of approach and separation of said arbors being the same. 1

15. A machine for finishing gears comprising a gear arbor, a tool arbor, means for supporting said arbors with their axes crossed at an angle less than 30', means for rotating one of said arbors, means for relatively translating said arbors in a plane parallel to the axes of both of said arbors to shift the bearing of said tool alternately from mid position toward either end of said gear teeth, means operable in accordance with said translation for causing said arbors to approach by increments, and other means for causing said arbors to approach gradually as said bearing shifts from mid position toward either end of said gear teeth and for causing said arbors to separate gradually as said bearing shifts from either end of said gear teeth centrally, said means being related so that said gradual approach and separation replaces, rather than is superimposed on, said incremental approach 18. A-machine for crowning the teeth of a gear which comprises a rotary tool support and a rotary gear support for supporting a' gearlike tool and a gear in mesh at limited crossed axes, whereby the tooth of said gear contacts the teeth of said tool at a limited area, means for rotating one of said supports to rotate said gear and tool together in meshed relation, means for relatively translating said supports in a plane parallel to the axes of both said tool and gear to cause the contact between said tool and gear teeth to move lengthwise of the teeth of said.

gear, andmeans automatically operated in accordance with said translation to feed said gear and tool gradually relatively towards and away from each other while preserving the relative orientation of the axes of said gear and tool in a manner to cause said axes to approach as the said contact shifts'fropi mid position on said gear teeth toward either end thereof, and to cause said axes to separate as the said contact shifts from either end of said gear teeth toward mid position thereon.

17. A machine for crowning the teeth of a gear comprising a work support adapted to mount a work gear for rotation, a tool support adapted to mount a gear-like tool for rotation in mesh with the work gear at limited crossed axes, one

of said supports being mounted for free rotation,

means for positively rotating said other support, means for slowly relatively reciprocating said supports in a plane parallel to the axes of both said work gear and said gear-like tool, and means automatically operated in accordance with said reciprocation for superimposing upon said relative reciprocation a gradual relative feed in a direction perpendicular to said plane of reciprocation, said feed being such as to cause the axes of said gear and gear-like tool to approach and separate gradually during relative reciprocation so as to form gear teeth of varying thickness.

18. A machine for finishing gears comprising a gear arbor, a tool arbor, means for supporting said arbors with their axes crossed at an angle less than 30 to position a gear and gearlike tool carried thereby in mesh, means for rotating one of said arbors, means for bodily moving one of said arbors in a curved path while maintaining the parallelism of the arbor axes an amount sufiicient to cause the contact between the teeth of the gear and gearlike tool to shift from end to end of the teeth of the gear, said path occupying the plane of said gear arbor and being concave in the directiontoward said tool arbor.

19. A machine for finishing gears comprising a rotary arbor for a gear, a rotary arbor for a gear-like tool, means for supporting said arbors with their axes crossed at an angle less than thirty degrees and with the gear in mesh with the tool, means for rotating one of said arbors, means for relatively translating said arbors to move the contact between the gear and tool teeth lengthwise of the gear teeth, means automatically operable in timed relation to the relative translation for relatively moving said arbors toward each other as the contact moves from mid-position toward either end of the gear teeth and away from each other as the contact moves from either and toward the mid-position of the gear teeth, and means for adjusting said automatic means to select the point in relative translation at which said relative movement of the arbors toward each other is initiated.

' ROBERT S. DRUMMOND. 

